As is known, the recycling of copper is very important because it is a metal whose natural resources are rather scarce and thus it has high price, and because of the energy and environmental advantages that are obtained.
Copper scraps are marketed all around the world, selected according to their origin and their content of pure copper.
For example, the following types of copper scraps are marketed:                Berry (First class), which consists of old and new cables made of pure non-tinned copper with a minimum of 99% Cu.        Clove, i.e., electric wires made of pure copper in granulate form with a minimum of 99% Cu.        Kanal, pure copper wires with a minimum content of Cu equal to 98%.        Birch, copper wires with welds and Cu content equal to 93-95%.        Candy (Second class)—telephone wires, copper plates, pipes with paint and paper. 95-96% Cu content.        Dream (Third class)—mixed scraps of unalloyed copper, with 92-93% Cu content.        
Such scraps may be recycled for electrical uses directly by fire refining.
Scraps with lower Cu content are melted and fire refined to produce anodes that are converted into cathodes by electrolysis in a subsequent treatment, or for the formation of alloys.
Both the melting operation and the refining operation are usually performed with reverberatory furnaces, with liquid or gaseous fuels, of the tank or tiltable type.
The uses of copper can be divided in two large categories: electrical and non-electrical. The former are the most important in economical and volume terms and require copper with high conductivity and therefore high purity (99.95% Cu).
The background art indicates, as starting material for producing electric wires, copper in form of cathodes obtained by electrolysis and thus 99.99% pure and with a conductivity above 101 IACS.
The cathodes are melted continuously in well-known tower furnaces or shaft furnaces (for example of the type disclosed in U.S. Pat. No. 3,199,977) and the like, which feed continuous casting and rolling plants in order to obtain so-called “ETP” rod coils in diameters comprised between 8 mm and 25 mm.
The rod is then cold-drawn in countless wires with different diameters, stranded and/or coated with insulator in order to obtain the desired wires. The rod may be also drawn or rolled in strips and shaped elements and may also be extruded continuously by using the Conform method.
Besides this technology, which meets most of the market needs, there is also a method for manufacturing rod for electrical uses that starts from scraps with a minimum Cu contents of 92%. Such rod is called FRHC (Fire Refined High Conductivity) and has characteristics that are almost identical to ETP rod.
This last method is based on a reverberatory furnace for the melting and refining of scrap, such operations being performed over 16 hours, while in the remaining 8 hours of the day the furnace feeds a casting and rolling line.
The reverberatory furnace for the above mentioned uses is a tank furnace, which can vary between less than 50 t and more than 400 t.
Such furnace is also used for the production of anodes for which it is loaded both with scraps and with Blister copper.
Such type of furnace, illustrated in FIGS. 1 to 3, has a furnace body 1 with a parallelepipedal shape with two mutually opposite heads 2, 3, or short sides, arranged along substantially vertical planes and mutually connected by a bottom wall 4, by an upper wall or ceiling 5 and by two side walls 6, 7. Such furnaces are provided with one or two burners 8 on a head 2 and with an outlet 9 for the exhaust gases to be connected to a stack on the opposite head 3. On one side wall 6 and in a central region one or two loading ports 10 are provided, which are closed by a corresponding movable door 11, while toward the end that is near to the outlet 9 for the exhaust gases, on the same side wall 6, a small door or deslagging door 12 is arranged which allows deslagging, i.e., the extraction of the slag 22 that floats on the bath 15 of molten metal.
On the other side wall 7 the casting spout 13 and the system of so-called “tuyeres” are provided, i.e., pipes 14 that supply both compressed air for oxidizing the bath 15 and fuel for deoxidizing the bath 15.
The whole furnace body 1, which is constituted by an outer structure 16 made of welded steel and by the inner refractory lining 17, can tilt about its own longitudinal axis 1a, which is horizontal and parallel to the longer sides of the furnace body 1, being provided, in the lower portion, with two or three crescent-shaped cradles 18, which can roll on a plane or on a system 19 of wheels or rollers. The oscillation of the furnace body 1 about the axis 1a is achieved by means of hydraulic cylinders 20, which are interposed between the furnace body 1 and the footing 21 that supports it.
The maximum rotation in order to empty the furnace, i.e., toward the side of the casting spout, is about 25°-30°, while the rotation in the other direction to facilitate deslagging is 5°-7°.
Another less used configuration is the one that provides for the lack of rolling cradles. In this case, tilting occurs about an horizontal axis on which two spherical joints or bearings are placed which are connected to the base of the furnace and are arranged on two strong supports; powerful hydraulic pistons, connected to the other side of the furnace in a suitable position, allow the movement of the furnace.
In order to withstand the aggression of oxygen, of oxides and of slag components it is necessary to use magnetite refractory, which however is sensitive to thermal shock and has a considerable linear expansion at high temperatures (even 10 cm for 10 meters of wall).
Due to these characteristics of the refractory and due to the movements necessary during the working cycle, particular care must be given to the structure of the walls and roof of the furnace.
In this type of furnace, a mix of scraps, loose, in bales or as blocks of blister copper, is loaded intermittently through the loading port and is simultaneously melted. For economic reasons, loose scrap is preferred in spite of the difficulties in handling.
This operation may last 6 to 18 hours and is very laborious; both with four-wheel frontal loaders with diesel engines and with expressly designed loading machines, insertion of the material is delicate both because the jambs of the door must not be damaged, both because each charge is limited in weight for the volumes of the loaded material, and because the charge must be distributed in the tank of the furnace, preventing it from accumulating only proximate to the door.
A first deslagging is then performed and one proceeds to the refining step.
Basic refining is performed by injecting air, i.e., oxygen which combines with the pollutant metals, forming oxides that float as slag and are then extracted from the bath. Each operator then adds other refining methods with the use of specific additives in order to extract rapidly particular pollutants such as Pb—Sn—Ni and others from the bath.
The last operation is the reduction of the oxygen content that is performed by injecting fuel from the tuyeres.
Once the desired level of oxygen has been stabilized and the last deslagging has been completed, one proceeds with casting, which can be aimed at obtaining anodes or continuous rod.
The most important limitations of this type of furnace are the difficult insertion of the scraps and the low thermal efficiency for copper melting; limitations set by the very geometry of the furnace.
In order to overcome such limitations, some types of furnace have been provided, both for primary metal and for impure metal or scrap, which combine some characteristics of the reverberatory tank furnace and some characteristics of the vertical furnace disclosed in U.S. Pat. No. 3,199,977 by A. J. Phillips et al. dated 1965, better known as tower furnace or vertical Asarco furnace, known as “shaft” furnace.
A combination of vertical furnace and tank reverberatory furnace is disclosed by E. De Bie in U.S. Pat. No. 3,715,203 dated 1973 and in Italian Patent IT-995947 by Giulio Properzi.
Furnaces known as Striko or the like have been in use already for a long time; however, the difficulty of melting impure copper or scrap with a Cu contents of less than 97% in a vertical or quasi-vertical furnace has not been overcome, because the slag that forms adheres to the refractory and blocks the lower outlet.
Small furnaces of the combined vertical-tank type under 50 t have been proposed, but to the detriment of the possibilities of tilting in both directions, which instead are very useful for the refining and casting operations.
It has been noted over time that the impure metal must be poured with its slag directly onto a large bath of molten metal, where the slag floats and can be extracted with the usual deslagging operations. The molten metal bath must have the maximum surface that complies with practicality criteria, because the thermal/chemical refining phenomena are linear with the surface of the bath; i.e., the greater the surface, the higher and faster the refining. Some attempts to arrange a turret acting as a vertical furnace above the ceiling of a classic reverberatory furnace have not yielded good results, because the turret fails both statically and during tilting and also due to excessively difficult loading.